Control Using Two Manipulated Parameters. 2006Fisher-Rosemount Systems, Inc. Slide 1-1 Control Using Two Manipulated Parameters

Transcription

1 Control Using Two Manipulated Parameters Slide 1-1 Control Using Two Manipulated Parameters

2 Introduction Overview Typical Examples Split-Range Control Concept, variations in implementation Setup in field vs. Splitter Block and IO for each valve. Using Splitter Block, Example. Valve Position Control Concept and typical implementation Setup of I-only control in implementation Impact of mode/status, Example. Combining Split Range and Valve Position Control How to implement in DeltaV Example Summary Slide 1-2

3 Control Using Two Manipulated Parameters SP One(1) Controlled Parameter Controller Unmeasured Disturbance Two(2) Manipulated Parameters Process Under specified problem that has multiple solutions for unlimited operation. Extra degree of freedom is used to achieve unique solution that satisfied specific control objective. Most common techniques are: split range, valve position control. Combination of these techniques offer new capability to address this class of problems Slide 1-3

4 Split Range Traditional Implementation TIC 101 Temperature Example 100 Valve Position (% of Span) ma IP PSI Cooling A/O Heating 3 Slide 1-4 A/C IP Output ( PSI ) 15 Process TT 101 Cooling Heating Sequencing of valve accomplished through calibration of positioner, selection of actuator (A/O or A/C) Pro Less expensive installation (1 pair of wires to field and 1 I/P) Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain. Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem. Con The actuator, pneumatic positioner, and I/P performance shift with time and field conditions Con I/P failure disables 2 valves. Replacements in the night may not have the special settings

5 Split Range Traditional Implementation AIC Valve Position (% of Span) 0 3 ph Example 4-20ma IP PSI A/O Coarse Valve PS 102 Slide 1-5 A/O Fine Valve I/P Output ( PSI )15 Process ph AT 102 Fine Valve Coarse Valve Sequencing of fine and coarse valve requires pressure switch, two solenoid valves and associated wiring and tubing Con Complex installation Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain. Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem. Con The switch, actuator, pneumatic positioner, and I/P performance shift with time and field conditions Con I/P failure disables 2 valves. Replacements in the night may not have the special settings

6 Split Range DeltaV Implementation AI PID SPLT AO AO Splitter bock is used to implement split range control. When using traditional valves, split range control may implemented in DeltaV Controller using two(2) current outputs AI PID SPLT AO AO Split range control may be partially or fully assigned to fieldbus devices. Slide 1-6

7 Split Range Control in DeltaV Slide 1-7

8 Splitter Block Calculation Slide 1-8

9 IN_ARRAY Parameter SP range associated with OUT1 SP range associated with OUT2 The SP range associated with each output is defined by IN_ARRAY. SP range of outputs may be defined to overlap The SP upper end of range must be greater that lower end of range for each output Slide 1-9

10 OUT_ARRAY Parameter OUT1 Range for associated SP range When SP is outside defined range, then the value at the end of range is used to determine the output. LOCKVAL determines if OUT1 value is held if SP is greater that the upper end of range defined for OUT1. No restrictions are placed on the output range. Slide 1-10

11 Splitter Block OUT_1 OUT_2 100 OUT_ARRAY IN_ARRAY OUT_ARRAY IN_ARRAY LOCK_VAL holds HYSTVAL LOCK_VAL is zero OUT_ARRAY IN_ARRAY Slide 1-11 SP

12 Slaker Heating/Cooing Example AI PID SPLT AO TT103 TIC103 FY103 IP103A AO IP103B FY 103 TIC 103 IP 103A HEATER IP 103B COOLER TT 103 Slide 1-12

13 Split Range Output (FY103) 100 Valve Position (% of Span) Cooling (IP103B) Heating (IP103A) 0 0 TIC103 Output (% of Span) 100 Slide 1-13

14 Steam Header Example AI PID SPLT AO PT104 PIC104 FY104 IP104A AO IP104B Boiler 1475# Header IP 104A FY 104 PIC 104 IP 104B PT 104 Turbo Generator Slide # Header

15 Split Range Output (FY104) - Capacity 100 Valve Position (% of Span) Valve 104A Valve 104B 0 0 PIC104 Output (% of Span) 100 Slide 1-15

16 Calculating Splitter SP Ranges Example: Steam flow to Header, splitter interfacing directly to PRV s, no overlap Valve 1 rating = 50kph Valve2 rating = 150kph Desired Splitter Span valve 1 = 100*(50/(150+50)) = 25% A 1% change in controller output to the splitter should have the same impact on control parameter when operating with either valve. When manipulating the same or similar material e.g. steam flow to header, then the range may be calculated based on valve rating. SP range for valve 1 = 0-25% SP range for valve 2 = % Tests may be performed to determine impact of each valve on the controlled parameter. Slide 1-16

17 Testing Process to Determine Splitter SP Ranges Example: Slaker feed temperature controlled using heating and cooling valves Controlled Temperature Heating 1% Cooling Time Slide degF 1% Desired Splitter Span cooling valve = 100*(2.2/( )) = 66% SP range for cooling valve = 0-66% SP range for heating valve = % 2.2degF With the process at steady state and AO s in Auto mode, determine the magnitude of change in the controlled parameter for a 1 percent change in each valve. Calculate the splitter SP span and range for each output based on the observed response

18 Example Split Range Slide 1-18

19 Response to SP Change Split Range Output To Large Valve/Small Valve Small Valve SP PV PID OUT Large Valve Slide 1-19

20 Split Range Strengths and Weaknesses Pro - Process operation in simplified since two actuators are treated as one control manipulated parameter. Pro immediate change in target actuator position can be achieved over the entire operating range independent of the size of change in the splitter SP Con To achieve stable control over the entire operating range, controller tuning must be established based on the slower responding manipulated parameter. Con- Does not take advantage of difference in resolution of actuator e.g. fine vs. coarse valve. Valve position control may be used in place of split range control when there are differences in dynamic response or resolution in actuators. Slide 1-20

21 Valve Position Control Traditional Implementation Mode AIC 106 Target Valve Position ph Example ZC 106 I-Only Controller IP 106B Time Slide 1-21 IP 106A A/O Coarse Valve Fine Valve Process ph Fine Valve Coarse Valve AT 106 Target Valve Position PID control is implemented using the actuator with finer resolution or fastest impact on controlled parameter The actuator with coarse resolution or slower impact on the controlled parameter is adjusted by an I-only controller to maintain the long term output of the PID controller at a given target I-Only controller must be disabled when the PID controller is not in an Automatic mode.

22 Valve Position Control DeltaV Implementation AI PID AO I-Only AO I-Only control is achieved by configuration of the PID Block STRUCTURE, GAIN and RESET parameters. Fieldbus devices AI PID Slide 1-22 AO I-Only AO Traditional field devices It is possible to implement valve position control in the DeltaV controller or for this function to be distributed to fieldbus devices.

23 Valve Position Control in DeltaV Actuator with fastest impact or highest resolution is used to maintain the controlled parameter at setpoint. The OUT of the PID used for control is wired to IN on the PID block used for I- Only regulation of slower responding or coarse resolution. PID configured for I- Only control Slide 1-23

24 Configuring PID for I-Only I Control The STRUCTURE parameter should be configured for I action on Error, D action on PV The GAIN should be set to 1 to allow normal tuning of RESET (even though proportional action is not implemented. RESET should be set significantly slower than that the product of the PID gain and reset time used for control e.g. 5X slower Slide 1-24

25 Precise Flow Using Big/Small Valve AI PID AO FT107 IP107A FIC107 I-Only ZC107 AO IP107B FT 107 FIC 107 ZC 107 IP 107A IP 107B Slide 1-25

26 Example -Boiler BTU Demand AI SUM PID AO FT109B AI FT109A FY109 FIC109 IP109A I-Only ZC109 AO IP109B BTU Demand FY 109 FIC 109 IP 109A FT 109B HI BTU Fuel Boiler FT 109A Slide 1-26 ZC 109 IP 109B Low BTU Waste Fuel

27 Example Reformer Air Demand AI PID AO FT110 IP110 FIC110 I-Only ZC110 AO SC110 ZC 110 FIC 110 Total Air Demand SC 110 IP 110 FT 110 Secondary Reformer Air Machine Slide 1-27

28 Example Valve Position Control Slide 1-28

29 Response to SP Change - Valve Position Control with Large Valve/Small Valve SP PV Coarse Valve Limited Fine Valve Target position for fine valve is 30%. When the fine valve saturates, then response is limited to be reset of the I-Only control Slide 1-29

30 Valve Position Control Strengths and Weaknesses Pro Immediate control response is based on actuator with finest resolution and/or faster impact on controlled parameter. Pro Actuator with coarse resolution or slower impact on controlled parameter is automatically adjusted to maintain the output of the controller output long term at a specified operating point. Con The controller output may become limited in response to a large disturbance or setpoint change. For this case, the dynamic response becomes limited by the slower tuning of the I-only controller. The features of split range control and valve position control may be combined to provide immediate response to large changes in demand while retaining the features of valve position control for normal changes. Slide 1-30

31 Combining the Best Features of Split Range and Valve Position Control A composite Block can be created that combines the features of split range and valve position control Support for BKCAL_IN and BKCAL_OUT can be implemented to provide bumpless transfer Slide 1-31

32 Composite Algorithm NORMAL CAS_IN T SP FILTER_TC Filter - - x + x OUT_1 MODE RANGE SPAN Scaling x OUT_2 BKCAL_IN1 Balance Calculation BKCAL_OUT BKCAL_IN2 Slide 1-32

33 Composite Implementation Parameters that must be configure are: FILTER_TC, SPAN (of SP), RANGE (of OUT1), and NORMAL (desired position ) The FILTER_TC should be configured similar to the reset time of the I-Only Controller that would be used for valve position control. Slide 1-33

34 Demo Composite Combining Valve Position and Split Range Control Slide 1-34

35 Example: Response to SP Change Small change SP, PV OUT of PID Fine Valve Coarse Valve Large change For small changes in SP or load disturbance, the response is similar to that provided by valve position control For large changes in SP or load disturbance, the immediate response is similar to split range control Slide 1-35

36 Summary Split range control allows fully dynamic response to major setpoint of load disturbance changes. Valve position control may be used to takes advantage of any difference in control response or resolution in the manipulated parameters. A composite block has been demonstrated that combines the best features of split range and valve position control. Slide 1-36